Magnetic resonance imaging (MRI) detects the faint nuclear magnetic resonance (NMR) signals given off by protons in the presence of a strong magnetic field after excitation by a radio frequency signal. The NMR signals are detected using antennae termed “coils”. The term “coil” is also commonly used to refer to the antenna(e) and its housing or support structure. Thus “coil” may refer to a structure that contains a number of coils. “Coil element(s)” is used to refer to the electrical part of the device, the radio frequency coil or antennae.
NMR signals are extremely faint. Sensitivity of a coil to these signals decreases rapidly with increasing distance between the coil and the volume of interest. Coils are therefore placed in close proximity to the region of interest of the imaged object. The size of the local coils is kept small to allow them to be easily fit to the patient on the MRI patient table and to enable imaging of only the imaging volume of interest, since imaging regions that are not required adds noise to the acquired signal unnecessarily. Coils local to the anatomy of interest tend to have a higher signal-to-noise ratio (SNR) than larger coils such as a “body coil” which is useful for obtaining large survey scans of the patient.
Use of MRI to distinguish pathologic tissue from healthy tissue has proven advantageous in some respects in comparison to other imaging modalities. For example, MRI uses non-ionizing radio frequency (RF) signals to acquire images, in contrast to the use of ionizing radiation used with computed tomography scanners. Moreover, MRI has shown improved sensitivity in comparison to other imaging modalities.
Various limitations, however, have impeded widespread adoption of the use of MRI for imaging portions of the body despite its advantages. One impediment is the cost of MRI equipment. MRI scanners are expensive. Body coils present numerous complexities and issues so local coils have developed to isolate regions of the body of interest, but MRI local coils also have cost concerns. Nonlimiting examples of MRI local coils include U.S. Pat. Nos. 7,379,769 and 7,970,452, commonly owned by the assignee for the present invention. For example, the housing of a local coil constrains resources. In addition, local coil designs often include multiple components that are complicated to assemble. The complicated assembly can affect precision and repeatability of assembly.
What is needed, then, is a MRI local coil design with fewer parts and repeatable assembly. The MRI local coil design is preferably cost-effective, reliable, easier and/or faster to manufacture, and/or easier and/or faster to assemble with more precision.